If you can wait, then wait. If not, then buy now.
Haswell will likely offer less than 10% performance increase over Ivy Bridge assuming the same clock speed. Intel is focusing more on lowering power consumption, than they are on increasing performance. That is just my opinion though. So far there is no solid data regarding performance.
I think Broadwell will offer a larger increase in performance. It will use the 14nm die process instead of 22nm which allows everything inside the CPU to be made smaller, thus consuming less power. At that point Intel can turn up the performance while still consuming the same amount of power as Haswell CPUs, or less.